Authorities: Lindsay Lohan violated 'several aspects' of probation

Investigators have been looking into claim that Lohan tussled with an employee

Officials expect a copy of the investigation to go to a district attorney's office this week

Authorities say the former staffer will "no longer be cooperating in the investigation"

Lohan is free to leave court-ordered rehab this week

Tune in to "Showbiz Tonight" at 5 p.m. and 11 p.m. ET on HLN for the latest on what could happen to Lindsay Lohan.

Los Angeles (CNN) -- Though she is free to leave court-ordered rehab for substance abuse this week, actress Lindsay Lohan's legal issues could get more complicated after police in California said she violated her probation.

The Riverside County Sheriff's Department said Lohan violated probation when she allegedly tussled with a then-staff member at the Betty Ford Center here as she was undergoing three months of court-ordered substance abuse rehab.

Authorities plan to send the result of their investigation to the district attorney's office to decide if the actress should face battery charges -- even though the former staff member has said she will no longer cooperate with the investigation and does not want charges filed, the department said Monday.

"It is expected that this investigation will be sent to the district attorney's office later this week," the sheriff's office added.

The Betty Ford Center fired the staffer, Dawn Holland, after information about the December 12 incident was leaked to the media.

"When patients come to the center for treatment, they come to a safe place where their identity is protected, where anonymity is safeguarded," the center said in a statement, without confirming Holland was the employee in question.

Holland has told investigators she will "no longer be cooperating with the investigation and does not wish to have charges filed," the sheriff's office said.

Last month, Lohan's lawyer Shawn Chapman Holley confirmed that an "incident" had taken place, but declined to comment on what happened.

Meanwhile, Holland's lawyer said last month that the former staffer was "targeted, unmercifully interrogated, intimidated and threatened with her livelihood" by the treatment center.

Lohan checked into the Betty Ford Center on September 27 after it became clear a judge intended to send her to jail because of a failed drug test.

The judge eventually ordered Lohan to stay in the drug rehabilitation program until Monday instead of going to jail.

Lohan's probation is scheduled to end in August of 2011.

Prosecutor Danette Meyers said she expects to see Lohan back in municipal court on February 1 for a review of whether she has fulfilled the terms of her probation.

Lohan's legal troubles began when she was arrested twice in 2007 on charges of driving under the influence; in the second incident, she was charged with cocaine possession.

Los Angeles Superior Court Judge Elden Fox has said if Lohan violates the rules of her rehab program or fails a drug test before her court date on February 25, she will be sent to jail for 180 days.

CNN's Alan Duke and In Session's Grace Wong contributed to this report.